A lean burn engine that is capable of carrying out a lean combustion mode in which a target air-fuel ratio is set on a lean side in comparison to a theoretical air-fuel ratio has been known. During lean combustion, the lean burn engine switches an air-fuel ratio to the theoretical air-fuel ratio on a rich side in comparison to the target air-fuel ratio of the lean combustion or a target air-fuel ratio therearound and carries out stoichiometric combustion in the event of, for example, acceleration, when engine torque falls short. The lean burn engine is equipped with an occlusion reduction-type NOx catalyst, and thus a rich spike is carried out so that the air-fuel ratio is temporarily switched toward the rich side and nitrogen oxide that the NOx catalyst occludes is purified. In a case where the operation mode is switched from the lean combustion mode to the stoichiometric combustion mode or the non-lean combustion mode in which the rich spike is carried out, the air-fuel ratio is reduced due to an increase in fuel quantity. Then, the engine torque increases.
The hybrid vehicle that is equipped with the lean burn engine can absorb the increase in the engine torque resulting from the switching of the operation modes through regenerative control in a motor generator. However, regeneratable torque regeneratable by the motor generator is limited, and thus the increase in the engine torque cannot be fully absorbed by the regeneration of the motor generator in some cases. For example, a control device for a hybrid vehicle in which surplus torque that exceeds required torque is absorbed by regeneration of a motor generator while an increase in engine torque that occurs during a rich spike is suppressed to the minimum by control for reducing engine power such as ignition retarding and EGR amount increase has been known (PTL 1). This control device also performs enhancement of charging capacity of a battery, by lowering an electric power storage rate of the battery, relaxing an input limit of the battery, and the like, in preparation for regenerative control by the motor generator. PTL 2 is also included in the patent literature associated with the invention.